Bedrock geologic map of the Old Fort 7.5-minute quadrangle, McDowell and Yancey counties, North Carolina

North Carolina Department of Environmental Quality Divison of Energy, Mineral and Land Resources S. Daniel Smith, Director Kenneth B. Taylor, State Geologist GEOLOGIC OVERVIEW CORRELATION OF MAP UNITS £ о => ш О < bzmp bzpg mx Mylonite / phyllonite Porphyroclastic biotite gneiss Mixed gneiss О О N О CC Ш н о (Г о. о ш Metasedimentary Rocks Metasandstone Zss Undivided Graphitic schist Amphibolite ш (5' § 5 ш ^ 5- ш 5' (Я INTRODUCTION The Old Fort 7.5-minute quadrangle lies in western North Carolina in portions of McDowell and Yancey counties. The town of Old Fort is the largest community on the quadrangle. Much of the quadrangle north of the town of Old Fort lies within Pisgah National Forest owned by the U.S. Forest Service. Major transportation corridors include Interstate 40, the Blue Ridge Parkway, and Highway 70. Major streams include the Catawba River and its tributaries Curtis Creek, Cane Creek, and Mackey Creek. Total elevation relief is 3,770 ft with a low of 1 ,330 ft along Cane Creek and a high of 5,100 ft on Black Ridge. Bedrock of the Old Fort quadrangle comprises the following units (from northwest to southeast): An undivided Neoproterozoic metasedimentary unit with interlayers of amphibolite and graphitic schist; a Neoproterozoic metasandstone; porphyroclastic biotite gneiss of unknown affinity; mylonite/phyllonite of the Brevard Fault Zone; and a mixed gneiss unit with several rock types including Tallulah Falls biotite gneiss, Ordovician Henderson Gneiss, and felsic gneiss. The Brevard Zone is a prominent NE-SW-striking feature on the Old Fort quadrangle. The Brevard Zone is a linear fault zone that extends from Alabama to Virginia. It has a complex history of multiple reactivations with the earliest movement during the Neoacadian orogeny. This first movement was ductile and high-temperature with an oblique to strike-slip motion. During the Alleghanian orogeny, the Brevard fault reactivated with ductile strike-slip motion reaching greenschist-facies conditions, and later, experienced brittle dip-slip motion (Hatcher et al. , 2007). In the Old Fort quadrangle, ductile shearing attributed to Brevard Zone deformation is observed in a zone up to 9 miles wide. Stratigraphic relationships are unclear but the oldest unit on the quadrangle is interpreted to be the porphyroclastic biotite gneiss. It outcrops in the center of the Old Fort quadrangle immediately northwest of the Brevard Zone mylonite/phyllonite unit. Porphyroclasts within the unit are granule- to gravel-sized and circular, tending to be less ovoid and less elongate in the foliation plane than outcrops of the Henderson Gneiss. This unit is of unknown age and affinity but projects along strike to the northeast into Mesoproterozoic gneisses mapped by Bryant and Reed (1970). Northwest of the porphyroclastic gneiss, the quadrangle is underlain by Neoproterozoic metasedimentary units possibly correlative with the Ashe and Alligator Back Metamorphic Suites. These rocks are thick sequences of complexly deformed and metamorphosed clastic sediments deposited in marine rift basins. Interspersed with these sediments are lesser amounts of mafic volcanic rocks and ultramafic rocks thought to have originated as oceanic crust at a spreading center (Misra and Conte, 1991; Raymond and Abbott, 1997). These metasedimentary lithologies were complexly deformed and metamorphosed to amphibolite facies conditions during Taconic orogenesis. The effects of Brevard Zone shearing increase from northwest to southeast within these units. The metasandstone unit does not contain schist, amphibolite, or garnet while the undivided unit contains schist, amphibolite, and garnet along with lithologies found in the metasandstone unit. This may represent a shift in depositional environment from shallower marine in the SE to deeper marine in the NW. Southeast of the Brevard zone, the mixed gneiss unit contains biotite gneisses of unknown affinity and may contain the Ordovician Henderson Gneiss. Intense deformation of the Brevard zone makes delineation and identification of the protoliths of the mixed gneiss unit difficult. Biotite gneisses within the unit are heterogeneous and contain local granule- to gravel-sized porphyroclasts, ribboned felsic layers, boudined pegmatite layers, and granitic orthogneiss. Portions of this biotite gneiss may be correlative to the Tallulah Falls Formation mapped to the SE by Bream (1999). Possibly interlayered within the biotite gneiss are intrusions of the Ordovician Henderson Gneiss, a large granitic pluton that extends from SC to the NC piedmont. In its type locality the Henderson Gneiss is homogeneous and contains plentiful K-feldspar augens that are elongate with the foliation. Moecher et al. (2011) determined the age of the Henderson Gneiss is 447.6 Ma. Mylonitic and non-mylonitic foliations within the quadrangle dominantly strike NE- SW and dip to the SE. The prominent fracture set strikes NW-SE and is steeply bzmp bzpg mx Zss WHOLE ROCK ICP ANALYSIS1 OF SELECTED SAMPLES SAMPLE2 BC79 NB73 NB43 NB130 NB105 NB278 NB148 BC255 BC247 NB21 з 224,781 N 224.199 N 223.952 N 220.115 N 218.419N 219.164N 216.016N 215.772 N 214.214N 213.927N COORDINATES 323,691 E 322.499 E 320.927 E 318.886 E 318.989E 323.890E 321 ,787 E 322.588 E 320,311 E 318.819E feldspathic feldspathic feldspathic feldspathic mylonitic biotite .... , . ROCK TYPE , . , schist/phyll . , . . ' . . biotite gneiss metawacke biotite gneiss metawacke metawacke J metawacke metawacke granitoid gneiss 3 3 MAP UNIT Zun Zun Zun Zun Zss bzpg bzpg bzpg bzpg bzpg MAJOR OXIDES IN PERCENT Si02 ai203 Fe203 MgO CaO Na20 K20 Ti02 P205 MnO Cr203 LOI4 SUM5 ELEMENTS IN PPM® Ba Ni Sc Be Co Cs Ga Hf Nb Rb Sn Sr Та La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Mo Cu Pb Zn Ni As Cd Sb Bi Ag Au Hg Tl Se Zgs Za DESCRIPTION OF MAP UNITS1 Mylonite / phyllonite — Intensely deformed rocks with unknown protoliths. Tan to light-gray to dark-gray to light- olive-gray, to greenish-gray; fine- to coarse-grained; lepidoblastic to porphyroblastic; strongly foliated; mylonitic, locally ultramylonitic, locally brecciated; consists of sericite, quartz, feldspar, biotite, chlorite, and accessory graphite, garnet, sulfides, magnetite, and opaque minerals. Lenticular muscovite-aggregate porphyroblasts flattened in the mylonitic foliation planes impart a distinctive “fish scale" or “button” appearance to phyllonites. Locally interlayered with porphyroclastic biotite gneiss, granitic orthogneiss, and felsic gneiss. Porphyroclastic biotite gneiss — Heterogeneous mix of porphyroclastic and porphyroblastic, mylonitic biotite gneiss, quartzo-feldspathic gneiss, granitic orthogneiss, felsic gneiss, phyllonite, mylonite, and amphibolite, with minor biotite metawacke and metasandstone. Protoliths unknown although tentatively correlated to Mesoproterozoic gneisses mapped along strike to the northeast. Biotite gneiss is typically light-gray to grayish- black; well foliated; locally protomylonitic to ultramylonitic; medium- to coarse-grained; inequigranular; 2-10 mm sized porphyroblasts and/or porphyroclasts; lepidoblastic; consists of quartz, plagioclase, biotite, potassium feldspar, muscovite, minor epidote, garnet, and titanite. Mixed Gneiss — Heterogeneous unit consisting of a biotite gneiss of unknown affinity, Henderson gneiss, granitic orthogneiss, and mylonite. Biotite gneiss — Dark-gray to grayish-black; fine- to coarse-grained; well foliated; protomylonitic to mylonitic; inequigranular; porphyroclastic with clasts up to 10 mm in diameter and locally porphyroblastic; layering includes ribboned felsic layers and some pegmatite boudins; consists of quartz, plagioclase feldspar, biotite, potassium feldspar, muscovite, and epidote, with minor titanite and garnet. May be correlative to the Tallulah Falls Formation. Henderson Gneiss — Medium-gray to medium-bluish-gray to mottled black and white; inequigranular; medium- to coarse-grained matrix with distinctive megacrysts (augen) of microcline variable in size and abundance; typically protomylonitic to mylonitic, to granoblastic to lepidoblastic; massive to well foliated; dominantly biotite granite that ranges to tonalite; consists of potassium feldspar, plagioclase, quartz, biotite, muscovite and sericite, epidote group minerals, opaque minerals, and trace amounts of titanite, zircon, and apatite; locally pegmatitic and migmatitic. Locally microcline augen exceed 2.5 cm in length. The augen structures are produced by a high temperature protomylonitic overprint. Radiometric age date of approximately 447 Ma (Moecher et al., 2011). Metasedimentary Rocks Metasandstone — Interlayered metamorphosed sandstones with compositions including arkosic arenite, biotite metawacke, and quartzite. Tan to medium-gray to light-green; fine- to medium-grained; foliated to locally mylonitic; equigranular to inequigranular; consists of quartz, feldspar, muscovite, biotite, and minor accessory minerals; notably does not contain schist, amphibolite, or garnet. Undivided — Heterogeneous unit consisting of interlayered layers and lenses of laterally and vertically grading sedimentary and mafic volcanic rocks metamorphosed to kyanite- and sillimanite-grade. Rock types include metawacke, arkosic meta-arenite, schist, graphitic schist, mylonite, phyllonite, biotite gneiss, and amphibolite. Thickness of layering ranges from centimeters to meters. Biotite metawacke — Medium-light-gray to medium-dark-gray; medium- to coarse-grained; foliated; protomylonitic to mylonitic; equigranular to inequigranular; granoblastic to lepidoblastic; locally migmatitic; consists of quartz, plagioclase feldspar, biotite, muscovite, garnet, epidote, sillimanite and/or kyanite, staurolite, chlorite, opaque minerals, trace potassium feldspar and zircon; thickness of layering ranges from decimeters to meters. Muscovite metawacke — Light-tan to light-gray; fine- to medium-grained; foliated; protomylonitic to mylonitic; granoblastic to lepidoblastic; consists of quartz, plagioclase feldspar, muscovite > biotite, sericite, chlorite, with minor amounts of garnet, potassium feldspar, titanite, apatite, and other accessory minerals; locally has millimeter scale “pin-striped" fabric. Arkosic meta-arenite — Tan to medium-light-gray to gray; medium-grained, equigranular to inequigranular, foliated; consists of quartz, feldspar, with minor amounts of muscovite, biotite, and other accessory minerals. Schist — Garnet-mica schist, muscovite schist, muscovite-biotite schist; very light-gray to greenish-gray to medium-gray; medium- to coarse-grained; well foliated and locally mylonitic; inequigranular; lepidoblastic; consists of muscovite, biotite, garnet, quartz, plagioclase feldspar, potassium feldspar, and minor accessory minerals; locally contains chlorite, staurolite, tourmaline, kyanite, graphite, and trace zircon. Graphitic schist — Dark-gray to greenish-gray to medium-gray; fine- to medium-grained; well foliated to mylonitic; equigranular to inequigranular; lepidoblastic to porphyroblastic; consists of muscovite, biotite, garnet, sericite, quartz, graphite, feldspar, chlorite, pyrite, and accessory minerals; interlayered with lesser amounts of metaarkose, metawacke, garnet-mica schist, and phyllite. Amphibolite — Dark-green to black; fine- to coarse-grained; weakly to strongly foliated; equigranular; granoblastic to nematoblastic; consists of hornblende, plagioclase feldspar, epidote group minerals, quartz, garnet, chlorite, relict pyroxene, titanite, magnetite, and opaque minerals. Can occur as a very minor rock type throughout the other map units, where it may represent a metamorphosed volcanic rock. ’Mineral abundances are listed in decreasing order of abundance based upon visual estimates of hand samples and thin-sections. SCHMIDT EQUAL AREA STEREONET DATA ,'fV v • ... \ ■ . . уШу •• • . \ гщт&\ ■ ТШ ■' • - 90 270 -90 VftASV.. . V 180 Equal area Schmidt Net projection of contoured poles to foliation. Foliation count 612. 180 Equal area Schmidt Net projection of contoured poles to joints and unidirectional rose diagram inset. Joint count 628. /%; ••• •• 270 - - 90 270 - - 90 Equal area Schmidt Net projection of contoured poles to mylonitic foliation. Mylonitic foliation count 468. 'Whole Rock Inductively Coupled Plasma - Atomic Emission/Mass Spectrometer analysis conducted by Bureau Veritas, 9050 Shaughnessy St, Vancouver, BC Canada V6P 6E5. 2Sample numbers correspond to thin section and whole rock sample localities shown on geologic map 3State Plane Coordinate System 4LOI = loss on ignition in percent 5SUM = Sum total in percent 6PPM = parts per million. Ni analyzed by Bureau Veritas LF200 and AQ200 procedures. REFERENCES Allmendinger, R. W., Cardozo, N., and Fisher, D., 2012, Structural geology algorithms:Vectors and tensors in structural geology: Cambridge University Press, 289 pp. Bream, B.R., 1999, Structural and Stratigraphic Relationships of Ortho- and Paragneisses Southwest ot Marion, North Carolina [Master’s Thesis]: Knoxville, University of Tennessee, 155 p. Bryant, B., and Reed, J.C., Jr., 1970, Geology of the Grandfather Mountain window and vicinity, North Carolina and Tennessee: U.S. Geological Survey Professional Paper 615, 190 p. map scale 1 :62,500. Butler, R., 1970, Geologic map ot the Old Fort Quadrangle, NC, Unpublished geologic map. Cardozo, N., and Allmendinger, R.W., 2013, Spherical projections with OSXStereonet: Computers & Geosciences, v. 51, p. 193 - 205, doi: 1 0. 1 016/j .cageo.2012.07.02 1. Hatcher, R.D., Jr., Bream, B.R., and Merschat, A.J., 2007, Tectonic map of the southern and central Appalachians: A tale of three orogens and a complete Wilson cycle, in Hatcher, R.D., Jr., Carlson, M.P., McBride, J.H., and Martinez Catalan, J.R., eds., 4-D Framework of Continental Crust: Geological Society ot America Memoir 200, p. 595-632, doi: 10.1130/2007.1200(29). Misra, K.C., and Conte, J.A., 1991, Amphibolites of the Ashe and Alligator Back Formations, North Carolina: Geological Society of America Bulletin, v. 103, p. 737-750. Moecher, D., Hietpas, J., Samson, S., and Chakraborty, S., 2011, Insights into southern Appalachian tectonics from ages of detrital monazite and zircon in modern alluvium, Geosphere; v. 7; no. 2; p. 1-19; doi: 10.1130/GES00615.1 Raymond, L.A., and Abbott, R.N., 1997, Petrology and tectonic significance of ultramafic rocks near the Grandfather Mountain Window in the Blue Ridge belt, Toe terrane, western Piedmont, North Carolina, In: Paleozoic Structure, Metamorphism, and Tectonics ot the Blue Ridge ot Western North Carolina, Carolina Geological Society Field Trip Guidebook p. 67-85. 180 Equal area Schmidt Net projection of bearing and plunge of fold hinges in blue and mineral lineations in red. Fold hinge count 43. Mineral lineation count 13. >> ro 5 к. cc CL 0) O) This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program. 35e45'0"N 224.411 — 220.411 — 216.411 — 35“37‘30"N B2"7'30'W 35°45'0"N — 224.411 — 216.411 82°15'0"W 319.233 323,233 A' 82"7'30'W 35"37'30"N Topographic base produced by the United States Geological Survey. Altered by the North Carolina Geological Survey for use with this map. North American Datum of 1983 (NAD83). World Geodetic System of 1984 (WGS84). Proj ection: State Plane №>rth Carolina FIPS 3200 (Meters) 4, 000- meter ticks: Sate Plane №nth Carolina FIPS 3200 (№ters) mN \ 0.5 SCALE 1:24 000 0 KILOMETERS 6° 40' 118 MLS 0° 41 1000 500 0 0.5 NETERS 0 1000 2000 ROAD CLASSIFICATION NORTH -CAROLINA Expressway Secondary Hwy Ramp Local Connector local Road 4WD 1000 1000 2000 3000 MLES 4000 5000 6000 7000 8000 90» 10000 QUADRANGLE IDCATION UTM GRID AND 2013 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET Imagery . NAIP, August 2012 - September 2012 Roads . €2006-2012 TomTom Roads within US Forest Service Lands . FSTopo Data with limited Forest Service updates, 2013 №mes . GNIS, 2013 Hydrography . National Hydrography Dataset, 2012 Contours . National Elevation Dataset, 2008 Boundaries . Census, BWC, IBC, USGS, 1972 - 2012 U.S. National Grid 100,000-m Square ID LV Grid Zone Designation 17S FEET CONTOUR INTERVAL 40 FEET NDFtTH AMERICAN VERTICAL DATUM OF 1988 This map was produced to conform with the №tional Geospatial Program USTopo Product Standard, 2011. A metadata file associated with this product is draft version 0.6.19 ф Interstate Route '( J) US Route Cj/ aate Route j — j FS Primary Route FS Passenger Route FSHigh Clearance Route 1 2 3 4 5 6 7 8 1 Miunt Mtchell 2 Celo 3 Little Switzerland 4 Nfontreat 5 Marion West 6 Black Nfountain 7 Mrffitt Hill 8 Sugar HU ADJOINING QUADRAMILES Check with local Forest Sendee unit for current travel conditions and restrictions. OLD FORT, NC 2013 Tl CD CD Sea Level Fault Contact T indicates motion toward viewer A indicates motion away from viewer NORTH CAROLINA Department of Environmental Quality Г I • _ interpretive patterns of subsurface foliation orientations rOrm Lines Based upon suriicial structural measurements Research supported by the U.S. Geological Survey, National Cooperative Geologic Mapping Program under STATE MAP (award number - G18AC00205, 2018). The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. Bedrock Geologic Map of the Old Fort 7.5-minute Quadrangle, McDowell and Yancey Counties, North Carolina By Bart L. Cattanach, G. Nicholas Bozdog, Sierra J. Isard, and Richard M. Wooten Geology mapped from July 2018 to June 2019. Map preparation, digital cartography and editing by G. Nicholas Bozdog, Bart L. Cattanach, and Sierra J. Isard 2019 This is an Open-File Map. It has been reviewed internally for conformity with North Carolina Geological Survey mapping standards and with the North American Stratigraphic Code. Further revisions or corrections to this Open File map may occur. Some station data omitted from map to improve readability. Please contact the North Carolina Geological Survey for complete observation and thin-section data. North Carolina Geological Survey Open File Report 2019-04 EXPLANATION OF MAP SYMBOLS CONTACTS Zone of Confidence: 300m Contact — Identity and existence certain, location accurate Contact — Identity questionable, existence certain, location accurate Strike-slip fault, right-lateral offset-identity questionable, existence certain, and location accurate. Arrows show relative motion Contact — Identity and existence certain, location inferred iiniiiii iiiiiiin iiiniiii iiiiiiiii iiiiiiin iiiiiiiii iiiiinii in ■ in mi и iniiiiii Gradational contact-identity and existence certain, location approximate Thrust fault (1 st option)/Strike-slip fault, right-lateral offset — Identity and existence certian, location approximate. Sawteeth on upper (tectonically higher plate). Arrows show relative motion PLANAR FEATURES (For multiple observations at one locality, symbols are joined at the "tail" ends of the strike lines) (Symbols in red taken from Butler, 1970.) У У /* V Inclined metamorphic or tectonic foliation — Showing strike and dip Inclined metamorphic or tectonic foliation, for multiple observations at one locality — Showing strike and dip Vertical metamorphic or tectonic foliation — Showing strike Vertical metamorphic or tectonic foliation, for multiple observations at one locality — Showing strike Inclined mylonitic foliation — Showing strike and dip Vertical metamorphic or tectonic mylonitic foliation, for multiple observations at one locality — Showing strike У / ,46 V/ У Small, minor inclined joint — Showing strike and dip Small, minor inclined joint, for multiple observations at one locality — Showing strike and dip Small, minor vertical or near-vertical joint, for multiple observations at one locality — Showing strike Inclined mylonitic foliation, for multiple observations at one locality — Showing strike and dip Vertical mylonitic foliation — Showing strike ^ Inclined generic foliation (origin not specified) — Showing 38 strike and dip LINEAR FEATURES (Symbols in red taken from Butler, 1970.) e j? Inclined aligned-mineral lineation — Showing bearing and plunge , ,8 Inclined slickenline, groove, or striation on fault / surface — Showing bearing and plunge j, 56 Inclined fold hinge of generic (type or orientation unspecified) У small, minor fold — Showing bearing and plunge * Inclined generic (origin or type not known or not specified) lineation ' or linear structure — Showing bearing and plunge /41 Inclined crenulation lineation — Showing bearing and plunge OTHER FEATURES о Float station 06 A Thin section and whole rock analysis sample location X Prospect (pit or small open cut) X Abandoned sand, gravel, clay, or placer pit X Abandoned open pit, quarry, or glory hole NATURAL RESOURCES MIC - Mica SDG - Sand and gravel STN - Stone METAMORPHIC AND TECTONIC CONDITIONS TRAVERSE MAP Hillshade derived from a six meter pixel resolution LiDAR (Light Detecting And Ranging) digital elevation model. Red lines show paths of field traverses. Old Fort 7.5-minute Quadrangle, Open File Report 2019-04